Editing Urethra (section)

== Structure ==
The urethra is a fibrous and muscular tube which connects the [[urinary bladder]] to the [[external urethral meatus]]. Its length differs between the sexes, because it passes through the [[penis]] in males.

=== Male ===

[[File:Gray1142.png|thumb|The human male urethra laid open on its anterior (upper) surface]]

In the human male, the urethra is on average {{convert|18|to|20|cm|in|0|abbr=off|sp=us}} long and opens at the end of the external urethral meatus.<ref name=Grays2016 />

The urethra is divided into four parts in men, named after the location:<ref name=Grays2016 />

{| class="wikitable"
! width=120|Region !! Description !! [[Epithelium]]
|-
 | [[Pre-prostatic urethra]] || This is the intramural part of the urethra surrounded by the internal urethral sphincter and varies between 0.5 and 1.5&nbsp;cm in length depending on the fullness of the bladder. || [[Transitional epithelium|Transitional]]
|-
 | [[Prostatic urethra]] || Crosses through the [[prostate gland]]. There are several openings at the posterior wall:
# the [[ejaculatory duct]] (2 lateral) receives [[spermatozoon|sperm]] from the [[vas deferens]] and ejaculate fluid from the [[seminal vesicle]]
# the prostatic sinus which has openings for several prostatic ducts  where fluid from the [[prostate]] enters and contributes to the ejaculate
# the [[prostatic utricle]], which is merely an indentation.
These openings are collectively called the verumontanum (colliculus seminalis).
The prostatic urethra is a common site of obstruction to outflow of urine in BPH patients 
| [[Transitional epithelium|Transitional]]
 |-
 | [[Membranous urethra]] || A short (1 or 2&nbsp;cm) portion passing through the [[External sphincter muscle of male urethra|external urethral sphincter]]. This is the narrowest part of the urethra. It is located in the [[deep perineal pouch]]. The [[bulbourethral glands]] (Cowper's gland) are found posterior to this region but open in the [[spongy urethra]]. || [[Pseudostratified columnar]]
 |-
 | [[Spongy urethra]] (or ''penile urethra'') || Runs along the length of the penis on its ventral (underneath) surface. It is about 15 to 25&nbsp;cm in length,<ref>{{Cite web | url=https://www.centerforreconstructiveurology.org/urethral-stricture/intro-anatomy/ |title = Male Urethra Function & Urethra Anatomy Pictures |website=Center For Reconstructive Urology |url-status=live |archive-url= https://web.archive.org/web/20230926133006/https://www.centerforreconstructiveurology.org/urethral-stricture/intro-anatomy/ |archive-date= Sep 26, 2023 }}</ref> with steady diameter of 6 mm,<ref name="lumen-urethra">{{cite web |author1=Arcot J. Chandrasekhar, M.D. |author2=Hema Chandrasekhar, M.D. |author3=Jennifer Lim-Dunham, M.D. |title=Urethra |url=https://www.meddean.luc.edu/lumen/meded/radio/curriculum/gu/urethra.htm |website=Atlas of Radiological images to support Anatomy |publisher=Chicago's Jeasuit University |access-date=9 June 2024 |language=en |date=13 October 2010 }}</ref> and travels through the [[corpus spongiosum]]. The ducts from the [[urethral gland]] (gland of Littré) enter here. The openings of the [[bulbourethral glands]] are also found here.<ref>Atlas of Human Anatomy 5th Edition, Netter.</ref> Some textbooks will subdivide the spongy urethra into two parts, the bulbous and pendulous urethra. The urethral lumen runs effectively parallel to the penis, except at the narrowest point, the external urethral meatus, where it is vertical. This produces a spiral stream of urine and has the effect of cleaning the external urethral meatus. The lack of an equivalent mechanism in the female urethra partly explains why urinary tract infections occur so much more frequently in females. || [[Pseudostratified columnar]] – proximally<p>[[Stratified squamous]] – distally</p>
|}

There is inadequate data for the typical length of the male urethra; however, a study of 109 men showed an average length of 22.3&nbsp;cm (SD = 2.4&nbsp;cm), ranging from 15&nbsp;cm to 29&nbsp;cm.<ref>{{cite journal |vauthors=Kohler TS, Yadven M, Manvar A, Liu N, Monga M |title=The length of the male urethra |journal= International Brazilian Journal of Urology  |volume=34 |issue=4 |pages=451–4; discussion 455–6 |year=2008 |pmid=18778496 |url=http://www.brazjurol.com.br/july_august_2008/Kohler_ing_451_456.htm |doi=10.1590/s1677-55382008000400007|doi-access=free }}</ref>

The urethra in male placental mammals is typically longer than in females.<ref name="Hamilton">{{cite book|author=Marvalee H. Wake|title= Homeopathic Care for Cats and Dogs: Small Doses for Small Animals |url= https://books.google.com/books?id=nwQ3TvOMWxwC&pg=PA206|year=1999|publisher=North Atlantic Books|isbn= 978-1-55643-295-8 |page=206}}</ref>

=== Female ===
In the human female, the urethra is about 4&nbsp;cm long,<ref name=Grays2016>{{Cite book|url=https://www.worldcat.org/oclc/920806541|title=Gray's Anatomy: The Anatomical Basis of Clinical Practice |publisher=Elsevier Limited |editor=Standring, Susan|isbn=9780702052309|edition=41st|location=Philadelphia|oclc=920806541|year=2016|chapter=Bladder, prostate and urethra|pages=1261–1266}}</ref><ref name="lumen-urethra"></ref> having 6 mm diameter,<ref name="lumen-urethra"/> and exits the body between the [[clitoris]] and the [[vaginal opening]], extending from the [[internal urethral orifice|internal]] to the [[external urethral orifice]]. The meatus is located below the clitoris. It is placed behind the [[symphysis pubis]], embedded in the anterior wall of the vagina, and its direction is obliquely downward and forward; it is slightly curved with the concavity directed forward. The proximal two-thirds of the urethra is lined by [[Epithelium#Stratified_epithelium|transitional epithelial cells]], while the distal third is lined by [[Epithelium#Cell_types|stratified squamous epithelial cells]].<ref>Manual of Obstetrics. (3rd ed.). Elsevier. pp. 1-16. {{ISBN|9788131225561}}.</ref>

Between the [[Superior fascia of the urogenital diaphragm|superior]] and [[perineal membrane|inferior fascia]] of the [[urogenital diaphragm]], the female urethra is surrounded by the [[urethral sphincter]].

The urethra in female placental mammals is typically shorter than in the male.<ref name="Hamilton"/>

=== Microanatomy ===
The cells lining the urethra (the [[epithelium]]) start off as [[Transitional epithelium|transitional cells]] as it exits the bladder, which are variable layers of flat to cuboidal cells that change shape depending on whether they are compressed by the contents of the urethra.<ref name=Wheaters2013>{{cite book |last1=Young |first1=Barbara |last2=O'Dowd |first2=Geraldine |last3=Woodford |first3=Phillip |title=Wheater's functional histology: a text and colour atlas.|publisher=Elsevier |location=Philadelphia |date=2013|isbn=9780702047473 |edition=6th|chapter=Male reproductive system|page=349}}</ref> Further along the urethra there are [[pseudostratified columnar epithelium|pseudostratified columnar]] and [[Stratified columnar epithelium|stratified columnar]] epithelia.<ref name=Wheaters2013 /> The lining becomes [[stratified squamous epithelium|multiple layers of flat cells]] near the end of the urethra, which is the same as the external skin around it.<ref name=Wheaters2013 />

There are small [[mucus]]-secreting urethral glands, as well as bulbo-urethral glands of Cowper, that secrete mucous acting to lubricate the urethra.<ref name=Wheaters2013 />

The urethra consists of three coats: muscular, erectile, and mucous, the muscular layer being a continuation of that of the bladder.

===Blood and nerve supply and lymphatics===
[[Somatic nervous system|Somatic]] (conscious) innervation of the [[External sphincter muscle of female urethra|external urethral sphincter]] is supplied by the [[pudendal nerve]].